that's a great question! i do two things, when sketching ideas, roll out left, which in and of itself is interesting, because that's sooooo not western. when i am working on multiple layers, i tear, and create registration marks.

Almost always tear off first. And for the last seven years I've been using my former-partner-still-BFF's method of getting if loose enough form the roll to grab" blowing into the space between the end of the sheet and the roll.